Classifications

• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02F—DREDGING; SOIL-SHIFTING
  • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
  • E02F9/26—Indicating devices
  • E02F9/264—Sensors and their calibration for indicating the position of the work tool
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02F—DREDGING; SOIL-SHIFTING
  • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
  • E02F9/26—Indicating devices
• • E—FIXED CONSTRUCTIONS
  • E02—HYDRAULIC ENGINEERING; FOUNDATIONS; SOIL SHIFTING
  • E02F—DREDGING; SOIL-SHIFTING
  • E02F9/00—Component parts of dredgers or soil-shifting machines, not restricted to one of the kinds covered by groups E02F3/00 - E02F7/00
  • E02F9/26—Indicating devices
  • E02F9/264—Sensors and their calibration for indicating the position of the work tool
  • E02F9/265—Sensors and their calibration for indicating the position of the work tool with follow-up actions (e.g. control signals sent to actuate the work tool)

Definitions

• the invention relates to a method for calibrating an angle sensor and a vehicle with an angle sensor.
• Work machines such as wheel type loaders include work tools which can be moved through a number of positions during a work cycle.
• work tools typically include buckets, forks, and other material handling apparatus.
• a typical work cycle associated with a bucket includes sequentially positioning the bucket and associated lift arm in a digging position for filling the bucket with material, e.g. soil or sand, a carrying position, a raised position, and a dumping position for removing material from the bucket.
• control levers can be mounted to an actuator, or at the operator's cabin or directly be connected to an electrohydraulic circuit for moving the bucket and/or lift arms.
• the operator must manually move the control levers to open and close hydraulic valves that direct pressurized fluid to hydraulic cylinders which in turn cause the implement to move.
• the operator moves the control lever associated with the lift arm hydraulic circuit to a position at which a hydraulic valve causes pressurized fluid to flow to the head end of a lift cylinder, thus causing the lift arms to rise.
• the hydraulic valve closes and pressurized fluid no longer flows to the lift cylinder.
• angle sensors can be provided for functions like end dampening, automatic positioning, geometric calculations, load calculations etc.
• US 6,912,455 B2 discloses a calibration method of a steering arrangement comprising a steering motor having end stops by correlating the steering motor angle and the handwheel angle every time the vehicle starts.
• WO 2004022411 A1 describes a power steering device for an electromechanically steered vehicle comprising a variable software end stop that is increased with increasing steering angle.
• a method for calibration of at least one angle sensor sensing an angular position of a pivotable element rotatable from a first position to a maximum position, wherein during an operation time of the pivotable element at least one adjustable angle corresponding to an extreme value of the angle sensor is automatically maintained or updated depending on at least one measured angle determined by the at least one angle sensor.
• a manual calibration of the at least one angle sensor can be avoided, as the method provides a self adapting calibration.
• the updated adjustable angle is preferably stored in a memory coupled to the at least one angle sensor, particularly in a control device controlling the angle sensor.
• the invention can be advantageously employed for all types of mobile applications where positioning is required, for instance for an articulated work machine.
• a "soft stop" function of such an articulated work machine can easily be adjusted by taking account of the updated adjustable angle.
• a "soft stop” function the rotational movement of the articulated element, e.g. a work tool pivotably attached to the work machine, is damped just before the mechanical stop (end position) of the angular movement is reached.
• the soft stop reduces the wear of the work tool, the joints, the bearing etc. If during the lifetime of the work machine the wear of the machine induces an increase of the measured angle, the calibration method allows for tracking the increase simultaneously.
• the angle sensor can be adaptively calibrated by updating the adjustable angles according to the measured angle when the end positions (mechanical stop) of e.g. hydraulic pistons change over time by wear.
• a manual calibration or manually initiated calibration is not necessary as the method can automatically calibrate the at least one angle sensor during the whole lifetime of a device, e.g. a vehicle such as a work machine, where the at least one angle sensor is coupled to.
• the maximum position of the pivotable element is represented by the extreme value of the angle sensor.
• the pivotable element is protected against abrupt termination of an angular movement at a mechanical stop.
• the adjustable angle can be chosen to be equal or larger than an initial angle, wherein initially at the beginning of the overall operational time of the pivotable element the initial angle is set as extreme value for the angle sensor corresponding to the initial maximum position of the pivotable element.
• the initial angle equals a nominal angle representing a nominal mechanical stop minus tolerances such as one or more tolerance values of at least one of tolerance in a mechanical linkage providing the rotatable movement, and/or a mechanical installation tolerance of the angle sensor and/or an electrical measurement tolerance of the angle sensor.
• the nominal mechanical stop can be a design value representing an estimate of the mechanical stop.
• the adjustable angle can be an angle value corresponding to an angle defined by a current mechanical stop of the pivotable element.
• a plausibility check can be performed regarding the measured angle before the adjustable angle is maintained or updated. This allows for eliminating sensor faults which may tamper the measurement.
• the adjustable angle can be updated with a value not exceeding a maximum angle if the measured angle is greater than the maximum angle.
• the maximum angle equals the nominal angle corresponding to the nominal mechanical stop plus one or more tolerance values of at least one of tolerance in a mechanical linkage providing the rotatable movement, and/or a mechanical installation tolerance of the angle sensor and/or an electrical measurement tolerance of the angle sensor.
• At least a tolerance in the mechanical linkage providing the rotatable movement of the pivotable element and/or a mechanical installation tolerance of the angle sensor and/or an electrical measurement tolerance of the angle sensor can be included.
• Electrical measurement tolerances include for example cable harness, sensor tolerances, connectors, A/D converter etc. Such one or more tolerances can be expressed as angle values and can add up to a reasonable maximum correction value. By keeping the adjustable angle below this maximum angle a mechanical damage by rotating or swivelling the element, e.g. a work tool or a steering etc., to a too large angle can be avoided.
• the current adjustable angle can be set to a default value if the measured angle is less than the actual adjustable angle and/or if the angle sensor is replaced.
• the current adjustable angle can be reset to the first maximum angle if the measured angle is less than the initial angle and/or if the angle sensor is replaced.
• the reset can preferably performed by operator or service input. This step can advantageously account for e.g. ageing of the angle sensor which can yield too small measured angle values.
• a reset is also advantageous if the angle sensor is replaced by a new one.
• the adjustable angle can be set equal to the measured angle.
• the current mechanical stop is updated in the angle sensor according to the wear of the elements.
• At least the initial angle of a first pivotable element can be varied dependent on a basis angle of a mechanically connected pivotable element.
• the tilt angle of a bucket connected to a boom is dependent on a lift angle of the boom.
• a lookup table can be provided comprising initial angles for one or more linked angles of the mechanically connected pivotable element depending on the basis angle of the mechanically connected pivotable element.
• a basis angle e.g. the tilt angle of a bucket connected to a boom depends on a linked angle, e.g. a lift angle of the boom.
• the lookup table values can be adapted to a change in the measured angle value.
• the one or more linked angles can be updated to a value not greater than a stop angle if the measured angle of the linked angle is greater than the stop angle.
• a lookup table it is also possible to calculate the respective angle by a formula expression such as a polynom or the like.
• a vehicle comprising at least one angle sensor which is calibrated according to anyone of the method steps described above.
• the vehicle can provide a soft stop function which is performed with an automatically updated angle sensor.
• a computer program comprising a computer program code adapted to perform a method or for use in a method according to anyone of the method steps described above when said program is run on a programmable microcomputer.
• the computer program can be adapted to be downloaded to a control unit or one of its components when run on a computer which is connected to the internet.
• a computer program product is proposed stored on a computer readable medium, comprising a program code for use in a method according to anyone of the method steps described above on a computer.
• the invention can be applied to wheel-borne vehicles, track-borne vehicles and vehicles running on rails or stationary work machines.
• the invention is particularly useful for mobile work machines, such as articulated haulers, wheel loaders, excavators etc.
• the invention can also be applied to passenger cars, trucks, buses and other road vehicles but is primarily favourable for use in applications suffering from high mechanical wear and poor tolerances, which is particularly the case in heavy duty machines such as construction equipment and the like.
• Fig. 1 an illustration of angles considered in a method according to the invention
• Fig. 2 a flow chart illustrating preferred steps of the method according to the invention
• Fig. 3 a schematic sketch of a wheel loader indicating mechanical dependencies of an adjustable angle corresponding to an extreme value of the angle sensor (tilt angle of a bucket) on a first angle (lift angle of a boom) of a mechanically connected element (boom).
• Fig. 1 shows an illustration of an initial angle ⁇ 0 , an adjustable angle y, i.e. an angle corresponding to an extreme value of an angle sensor, and a maximum angle ⁇ considered in a method according to the invention.
• an articulated work machine (not shown) has one or more physical limitations, i.e. a mechanical stop, referred to by the adjustable angle Y which is corresponding to an extreme value of the angle sensor.
• the mechanical stop, i.e. the adjustable angle Y can change, particularly increase, over time due to e.g. wear.
• a control system controlling the articulated movement, e.g. tilting of the pivotably part, by help of one or more angle sensors preferably assumes that the extreme values for an angle sensor is an initial angle ⁇ o.
• the one or more angle sensors can preferably be arranged close to the pivot joint of the pivotable part.
• the initial angle ⁇ 0 is equal or less than a mechanical stop, i.e. an end position, for the work machine, particularly for the pivotable element of the work machine.
• the initial angle ⁇ o preferably includes tolerances in the mechanical linkage providing the rotatable movement, and/or a mechanical installation tolerance of the angle sensor and/or an electrical measurement tolerance of the angle sensor.
• the initial angle ⁇ o is selected so that it is always within the mechanical stop, which corresponds to the second angle y which can increase over time.
• the adjustable angle Y increases from the initial angle ⁇ o at the beginning, which represents the minimum value for ⁇ ; to the maximum angle ⁇ , which represents the maximum value for the adjustable angle y.
• the one or more angle sensors will detect measured angles ⁇ m of the pivotable element which become larger and larger with time and become greater than the initial angle ⁇ o.
• the adjustable angle Y for the angle sensor will be automatically updated and thus increase with time.
• the soft stop function can be activated a little bit too early for a new work machine or a replaced part which is subject to the soft stop function.
• this initial angle ⁇ 0 can be exceeded with the mechanical linkage. Consequently, the soft stop function will after some time of usage be activated at the right angle and at the right time.
• a limit value of the maximum angle ⁇ can be set which prevents the second angle Y from increasing indefinitely. For instance, if an angle greater than ⁇ is detected the adjustable angle Y will not be updated to a value greater than ⁇ .
• the maximum angle ⁇ is preferably equal to a nominal angle representing a nominal mechanical stop plus a tolerance in the mechanical linkage providing the rotatable movement, and/or a mechanical installation tolerance of the angle sensor and/or an electrical measurement tolerance of the angle sensor.
• the adjustable angle Y varies between the initial angle ⁇ o as minimum value and the maximum angle ⁇ as maximum value.
• the initial angle ⁇ o preferably includes tolerances for e.g. the mechanical linkage providing the rotatable movement and/or a mechanical installation of the angle sensor and/or an electrical measurement of the angle sensor and the like.
• the pivotable element must not be moved to a larger angle than the adjustable angle Y.
• the initial angle ⁇ 0 is an initial value for the mechanical stop in an early stage of the lifetime of e.g. an articulated work machine such as a construction equipment or the like.
• the initial angle ⁇ o is equal or below the second angle y.
• step 202 during operation of the pivotable element, the angle sensor detects a measured angle ⁇ m as extreme value for the rotation of the pivotable element.
• step 204 the measured angle ⁇ m is compared to the adjustable angle y. If the measured angle ⁇ m is not larger than the adjustable angle y ("no" in the flow chart), an update of the adjustable angle y is either not necessary or a fault is present which may make necessary a reset of the adjustable angle y to a start default value, particularly ⁇ o. Thus, the procedure jumps to the step 212.
• step 212 it is checked whether a measured angle ⁇ m has been compared to the adjustable angle y. Preferably this comparison is done continuously for every new measured angle during operation of the machine and the process can restart with step 200.
• step 212 it is checked whether a measured angle ⁇ m has been compared to the adjustable angle y. Preferably this comparison is done continuously for every new measured angle during operation of the machine and the process can restart with step 200.
• the adaptation of the adjustable angle Y to increasing values of the end position of the pivotable element can be monitored continuously during operation of the element. Alternatively, monitoring can be performed periodically and/or depending on how the pivotable element is used. According to a preferred development of the method mechanical dependencies can also be considered. This is illustrated in Fig. 3.
• Mechanical dependencies can occur, for instance, in a lifting framework of a wheel loader 100 where the mechanical stop for the tilt angle ⁇ tilt of a bucket 104, is dependent on a lift angle ⁇ lift of a boom 102 on which the bucket 104 is arranged in an articulated manner via struts 106, 108.
• the lift angle ⁇ lift is a basis angle to which the tilt angle ⁇ tilt is linked. A variation of the basis angle alters the linked angle.
• the initial angle ⁇ 0 is different for each value of the basis angle, i.e. the lift angle ⁇ lift.
• the lower end of the bucket is tilted by an angle ⁇ b with respect to the horizontal direction defined by the centers of the wheels of the wheel loader (indicated by a line through the wheel enters in the drawing).
• the tilt angle ⁇ tilt of the bucket 104 is the angle between the boom axis 110 and the first strut 106.
• the angle ⁇ b of the lower side of the bucket 104 is changed by varying the tilt angle ⁇ tilt of the bucket 104.
• the tilt angle ⁇ tilt of the bucket 104 varies for varying lift angles ⁇ lift of the boom 102.
• Angle sensors 10a, 10b, 10c are located at positions along the boom 102, preferably pivot joints of the boom 102, the first strut 106 at the boom 102 and the bucket 104 at the boom 102, to detect angular movements of the boom 102, the first strut 106 and the bucket 104.
• the initial angle ⁇ 0 is now provided in a default lookup table comprising different values for the initial angle ⁇ ofor the tilt angle ⁇ tilt (linked angle) depending on the basis angle, i.e. the boom lift angle ⁇ lift.
• This default lookup table is updated when the angle G 0 is exceeded for each lift angle ⁇ lift.
• the angle ⁇ lift corresponds to the adjustable angle y in the flow chart in Fig. 2.
• an absolute limitation of the linked angle ⁇ lift can be used, for instance by providing a maximum angle ⁇ tilt.
• the default lookup table may contain any appropriate number of positions of lift angles ⁇ lift.
• a skilled person may also apply any appropriate interpolation between these angles ⁇ lift.
• the calibration method provides updating the first maximum angle ⁇ oto a greater value than the preceding value.
• the initial angle ⁇ 0 shows generally an increasing value.
• the adjustable angle y may be reset to an initial value of the initial angle ⁇ o and can then increase in value over time again.
• a reset of the current adjustable angle y to a default initial angle ⁇ 0 can be performed.
• the default initial angle ⁇ 0 is preferably the minimum of the adjustable angle Y and is preferably equal to the value after production of the work machine and/or the pivotable element, whichever value may apply.
• the reset can be done with an appropriate Human Machine Interface (HMI), for example in a menu on a display with one or more control buttons to press for initiating the reset.
• HMI Human Machine Interface
• the work machine, particularly a controller can then again update extreme values of the initial angle ⁇ o over time.
• the same reset procedure can be advantageously applied if an angle sensor is replaced by a new one, or the pivotable element or the mechanical linkage is replaced.
• the invention can be embodied as hardware, as software or in combination as both hardware and software.
• the invention is implemented in software, which includes but is not limited to firmware, resident software, microcode, etc.
• the software can be coupled to a control system for the one or more angle sensors.
• the method according to the invention can also be comprised in a computer program product accessible from a computer-usable or computer-readable medium, such as e.g. an electronic, magnetic, optical, electromagnetic medium, providing a program code for use by or in connection with a computer or any instruction execution system.
• a computer program product accessible from a computer-usable or computer-readable medium, such as e.g. an electronic, magnetic, optical, electromagnetic medium, providing a program code for use by or in connection with a computer or any instruction execution system.
• the computer program comprising a computer program code is adapted to perform the said method or for use in said method when said program is run on a programmable microcomputer.
• the computer program can be adapted to be downloaded to a control unit or one of its components when run on a computer which is connected to the internet.
• a computer program product can be stored on a computer readable medium, comprising a program code for use in the described method on a computer.
• the invention is favourably applicable particularly to all types of construction equipment and similar applications, for example steering, lift framework, suspension, load carrying structure etc. which employ one or more angle sensors for detecting an angular movement of a work tool or the like.

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• Engineering & Computer Science (AREA)
• Mining & Mineral Resources (AREA)
• Civil Engineering (AREA)
• General Engineering & Computer Science (AREA)
• Structural Engineering (AREA)
• Operation Control Of Excavators (AREA)
• Length Measuring Devices With Unspecified Measuring Means (AREA)

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• 2008
  • 2008-11-26 EP EP08878475.6A patent/EP2370644A4/de not_active Withdrawn
  • 2008-11-26 WO PCT/SE2008/000658 patent/WO2010062222A1/en active Application Filing
  • 2008-11-26 US US13/131,268 patent/US20110301781A1/en not_active Abandoned
  • 2008-11-26 CN CN2008801321125A patent/CN102245841A/zh active Pending

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